The present invention relates to a lactitol trihydrate crystal, a crystalline mixture solid containing it and a process for preparing them.
Lactitol is a product of lactose of which glucose moiety has been reduced into sorbitol and is designated as 4-.beta.-D-galactopyranosyl-D-sorbitol.
Lactitol and conventional methods for producing it are described in J. Agricultural and Food Chemistry, 27, 4, 680-686 (1979), in which a 30-40% by weight aqueous lactose solution as a starting material is hydrogenated under the condition of hydrogen pressure of 40 atm at 100.degree. C. in the presence of Raney nickel and the catalyst was then settled and removed by filtration to give a product after purification with ion exchange resin or activated carbon, etc.
Lactitol thus obtained has a relative sweetness of 36% on comparison based on the 100% of a 5% aqueous sucrose solution with a lactitol solution having the same concentration, and the sweetness of lactitol is lower than that of sorbitol (relative sweetness 65%) or xylitol (relative sweetness 96%).
West-German Patent (MEIZENA, 1974) discloses that lactitol is hydrolyzed with .alpha.-glucosidase (maltase) substantially slower than lactose or maltose.
For instance, lactose is hydrolyzed almost completely by .beta.-galactosidase within 45 min, while lactitol is hydrolyzed only to a level of 10-15% within 45 min.
Thus, lactitol is hardly absorbable and utilizable in the digestive system or scarcely fermented by intrabuccal bacteria, so that it is soluble for a sweetening source of low-caloric foods, dietary foods, low cariogenic foods, health foods or the like which are ingested by diabetics, obese persons or those who are cautious of diseases in adults or dental caries.
Lactitol has a hygroscopicity lower than sorbitol, glycerol, xylitol or the like and, as aldehyde group being reduced, stability to heat or alkali, so that it can be advantageously used for a variety of foods.
Lactitol crystals are described in several literatures. For example, a crystal of lactitol dihydrate having a melting point of 76-78.degree. C. and a specific rotation of +12.2.degree. C. and an anhydrous crystal of lactitol having a melting point of 146.degree. C. and a specific rotation of +14.degree. C. are described in Comptes Rendus Hebdomadaries des Seances de 1'Academie des Sciences, 170, 47-50 (1920) and J. Am. Chem. 74, 1105 (1952).
Moreover, a crystal of lactitol monohydrate is described in J. Agricultural and Food Chemistry, 27, 4, 680-686 (1979), in which a crystal of lactitol containing 1% of lactulitol (4-.beta.-D-galactosyl-D-mannitol) and 3% of mannitol is disclosed.
However, conventional anhydrous crystals of lactitol, lactitol monohydrate, lactitol dihydrate and methods for producing them have a variety of disadvantages in the production or application, and it has been earnestly desired to eliminate these disadvantages.
That is to say, the anhydrous crystal of lactitol in the prior art has many problems (i) in production that a relatively difficult drying process or tedious procedures are required; (ii) in properties that the anhydrous lactitol is relatively hygroscopic and absorbs humidity in the atmosphere to deteriorate its quality with the passage of time when such a packaging material or a container as used in other anologous sugar alcohols such as an anhydrous crystal of maltitol or the like are used; or (iii) in application that the anhydrous lactitol has a high melting point, and it should be heated to a high temperature when it is used as a dispersant of other powdered materials, so that the other components tends to be decomposed.
On the other hand, the lactitol monohydrate crystal which has hitherto been known in the art has problems that it contains impurities such as mannitol, lactulitol or the like and has bitter taste, so that it is not suitable for food, that it has a high melting point in the range of 94-97.degree. C. and thus feels rough at a temperature of ca. 60.degree. C. or that when the preparation of the crystal is tried for the reproduction test of it, the quality control of it is hard.
Moreover, dihydrate crystals of lactitol has also problems that it has the melting point of 76-78.degree. C., which is too high for the crystals to be dissolved when powdered on a warm food on a table, or that it has rough mouth feel and thus has an undesirable feeling on eating, so that the use of it for food are restricted.
Thus, there have been desired the improvements of the aforementioned problems for the crystals of lactitol.
We have investigated the physicochemical properties of lactitol for a long period and conducted earnest researches after the crystals of lactitol having excellent properties.
As a result thereof, we have discovered, upon crystallization of lactitol from an aqueous lactitol solution, the trihydrate crystal of lactitol which has been described in no literature and has excellent properties for applications, a crystalline mixture solid containing it and a process for producing them, and we have succeeded in the advantageous production of the trihydrate crystal of lactitol and the crystalline mixture solid containing it in an industrial scale. Thus, we have accomplished the present invention.